1. Field of the Invention
The invention relates to a method of manufacturing alkylphenols using a highly active aluminum-containing homogeneous catalyst and the catalyst itself. In particular, the present invention relates to a method of manufacturing alkylphenols wherein alkylation of phenol, or particularly of 2-alkylphenols by an alkene proceeds more rapidly, and at lower temperatures and pressures, than with ordinary aluminum phenolate catalysts.
2. Discussion of the Background
Ortho-substituted and di-ortho-substituted alkylphenols can be obtained by addition of alkenes to phenol, 2-alkylphenols, and other hydroxyaromatics, in the presence of aluminum phenolates (see Ullmann, 1979, "Enzyklopaedie der Technischen Chemie", V. 18, pp. 200 ff.). Ordinarily these reactions occur at a temperature of at least 100.degree. C. and possibly under elevated pressure. The optimal temperature region which is selected in each case depends on the groups connected to the C.dbd.C bond in the alkene which is undergoing chemical addition. The alkyl group formed is always branched to a very high degree (see Ullmann, loc.cit.). Isobutene and other alkenes which lead to formation of tertiary alkyl substituents are particularly reactive. Thus, the addition of isobutene to phenol or 2-tert-butylphenol is generally carried out at 110.degree.-120.degree. C. under an elevated pressure of up to 25 bar, whereas for alkenes such as propene, cyclopentene, or cyclohexene, reaction temperatures of &gt;180.degree. C. are required.
The aluminum phenolate catalyst is obtained by dissolving 1-3 wt. % aluminum in the phenol which is to be alkylated (see U.S. Pat. No. 2,831,898, Ger. Pats. 944,014 and 1,044,825; J. Org. Chem., 22, 1957, 642; and Anqew. Chem., 69, 1957, 699). It can also be obtained by reacting aluminum alcoholates or organoaluminum compounds with the phenol, or by other methods. The aluminum phenolates are known to have the highest selectivity and activity among the number of metal phenolates discussed in the patent literature. However, they also must be used in relatively large amounts in order to achieve economically important space yields per unit time.
Another disadvantage of the known methods is that prior to distilling the reaction product, one must deactivate the large amounts of the only moderately active aluminum trisphenolate catalyst. Environmentally safe disposal of the resulting wastewaters containing aluminum compounds and (alkyl)phenols presents further problems. An indication of the importance of this is the number of patent applications which have been and continue to be filed which are concerned with deactivation of the catalysts and decontaminating the wastewaters and/or reducing the amount of wastes (see, e.g., U.S. Pat. No. 3,200,157, Ger. Pat. 1,809,555, Ger. OS 20 039 062, U.S. Pat. No. 3,939,215, Ger. Pat. 26 02 149, Belg. Pat. 842,691, and U.S. Pat. Nos. 3,652,685 and 3,970,708). The problems associated with wastewater disposal have not been solved by changing to heterogeneous versions of the known catalysts (see Eur. Pat. 0,206,085), because the catalytically active aluminum phenolate catalysts are still carried away with the reaction products, in significant amounts.
There have been only a few proposals of measures for increasing the above-mentioned moderately low activity of the aluminum trisphenolate catalysts to any appreciable degree. The addition of metal halides, in particular alkali chlorides, earth alkali chlorides, and aluminum chlorides has been reported as advantageous (Ger. Pat. 1,044,825). Additionally, the use of alkyl halides (U.S. Pat. Nos. 3,426,082 and 3,200,157), alkali phenolates (Fr. Pat. 1,331,450, and Jap. OS 61-000,036 (in CA 104, 1986:186,127)), and cocatalysts comprising nitrogen and/or phosphorus (Jap. OS 60-218,346 in CA 104, 1986:88,273) can be effective. However, these examples suffer from the disadvantages of requiring unchanged high reaction temperature and/or pressures and of producing increased amounts of undesirable para-alkylphenol isomers. Thus the above-mentioned additives have not achieved any appreciable commercial success.
The only case of a catalyst active below 100.degree. C. is that of organoaluminum compounds, particularly alkylaluminums, combined with 2-tert-butylphenol (U.S. Pat. No. 3,355,504). With this system, isobutene is chemically added to 2-tert-butylphenol (used instead of phenol), at temperatures as low as 10.degree. C. Despite the low reaction temperature, the alkylation proceeds rapidly, to give the desired 2,6-di-tert-butylphenol, with relatively small amounts of undesired byproducts, such as 2,4-di-tert-butylphenol and 2,4,6-tri-tert-butylphenol while using amounts of catalyst comparable to the amounts of the higher temperature catalysts mentioned above (c. 1-3 mol % based on the amount of 2-tert-butylphenol used). However, as with other known phenol alkylation catalysts, this special system must be deactivated prior to product refinement. Otherwise dealkylation and transalkylation occur during the distillation.
The selectivity, yield and economic efficiency of the formation of 2,6-di-tert-butylphenol from phenol and/or 2-tert-butylphenol may be substantially increased above that offered by the above-mentioned state of the art, by various known methods (Eur. OSS 0,347,709 and 0,347,710, and especially Ger. Pat. 39 41 472). In each case the use of the known catalysts is recommended.
Most of the state of the art methods use catalysts having relatively low activity, which require the use of high temperatures. This results in the following disadvantages: large amounts of undesired byproducts and difficulty in disposal of large amounts of deactivated catalyst.